KR20090025439A - Oxygen sensor diagnosis method in an engine - Google Patents

Abstract

An engine oxygen sensor diagnosis method is provided to determine normality and abnormality of an oxygen sensor based on average diagnosis index dividing sum thickness real section with sum diagnostic standard time. An engine oxygen sensor diagnosis method comprises: a step for calculating: a corresponding revolution per minute; a thickness section(T_NOR_RICH) of a normal oxygen sensor at load; a diagnostic standard time(T_MAX) which is calculated by adding response delay time(T_DLY) of the oxygen sensor; and a sum diagnostic standard time(SUM_T_MAX) and a sum thickness real section(SUM_T_REAL) respectively; a step for calculating the average diagnosis index by dividing the sum thickness real section with the sum diagnostic standard time; and a step for determining normality and abnormality of the oxygen sensor according to whether the average diagnosis index exceeds 1 or not.

Description

Oxygen Sensor Diagnosis Method in an Engine

The present invention relates to a method for diagnosing an oxygen sensor of an engine, and more particularly, to a technology for determining whether an oxygen sensor is normal or abnormal using an output cycle of an oxygen sensor.

The vehicle should be equipped with a self-diagnosis system (OBD) in order to respond to environmental regulations, and this self-diagnosis system is to diagnose and inform the driver whether the parts related to exhaust gas are operating normally. Oxygen sensor is related to the air ratio control of the engine and is very important because it has a large impact on the exhaust gas.

The output of the oxygen sensor periodically moves up and down around the air ratio 1, and the cycle varies depending on the engine speed and the load (intake air volume), and shows a constant cycle for each engine speed and the load.

Therefore, when the oxygen sensor is abnormal, since the output of the oxygen sensor is generated at a period longer than that in the normal case, the self-diagnosis of the oxygen sensor is performed using such characteristics.

Referring to FIG. 1, an output signal of an oxygen sensor based on an air ratio 1 is shown below, where a is a rich section (T_NOR_RICH) of a normal oxygen sensor, b is a lean section (T_NOR_LEAN), and c is a normal oxygen sensor. The response delay time (T_DLY) of the oxygen sensor, which is the standard of error determination, d is a + c, and represents the reference time (T_MAX) of the oxygen sensor diagnosis.

Here, the oxygen sensor diagnostic index (VLS_CYC_AFR) may be calculated by the following equation 1 considering only the rich section of the oxygen sensor.

Here, T_REAL represents the rich section of the oxygen sensor actually measured.

In the related art, the oxygen sensor diagnosis index is calculated by a predetermined number of times or more, and the average diagnosis index (VLS_CYC_AFR_MV) is calculated and averaged. If the average diagnosis index (VLS_CYC_AFR_MV) is 1 or more, the oxygen sensor is diagnosed as abnormal. have.

That is, referring to FIG. 2, each time the oxygen sensor satisfies the diagnostic condition while increasing the counter by 1, the oxygen sensor diagnosis index is calculated and the cumulative diagnosis index is calculated. When the counter reaches the target value, the cumulative diagnosis is performed by the counter. The average diagnostic index (VLS_CYC_AFR_MV) is obtained by dividing the exponent to determine the normal abnormality according to whether or not it is more than one.

Here, the rich section T_NOR_RICH of the normal oxygen sensor is a constant value for a constant engine speed and load, but changes according to the change in engine speed and load, and the response delay time T_DLY is an exhaust gas regulation value. In consideration of the change in the engine speed and the load, it is fixed.

Therefore, when the oxygen sensor diagnosis index (VLS_AFR_CYC) is obtained from the rich section T_REAL of the actual oxygen sensor measured under the condition that the engine speed and the load are changed, the rich oxygen sensor's richness with respect to the diagnosis reference time T_MAX is obtained. The ratio of the section T_NOR_RICH changes for each calculation of the oxygen sensor diagnosis index VLS_AFR_CYC, and each oxygen sensor diagnosis index VLS_AFR_CYC is large and small as the diagnosis reference time T_MAX becomes the reference for the delay of the same oxygen sensor. Appears differently and the average diagnostic index (VLS_CYC_AFR_MV) is affected.

That is, if the diagnosis example in the vehicle is as shown in Table 1 below,

Load (air volume) 100 150 200 250 300 350 T_MAX (s) 0.98 0.67 0.56 0.46 0.39 0.39 T_REAL (s) 0.78 0.47 0.46 0.56 0.49 0.49 T_REAL-T_MAX (s) -0.15 -0.15 -0.15 0.1 0.1 0.1 VLS_CYC_AFR 0.846939 0.776119 0.732143 1.217391 1.25641 1.25641

As the average diagnostic index (VLS_CYC_AFR_MV) = ΣVLS_CYC_AFR / 6 = 1.014> 1, it is determined that the oxygen sensor is abnormal.

However, in practice, when the individual oxygen sensor diagnosis index (VLS_CYC_AFR) exceeds 1, it is 3 times and the difference between T_REAL and T_MAX is 0.1s in each case. The remaining three times, the oxygen sensor diagnostic index (VLS_CYC_AFR) did not exceed 1 and is 0.15s smaller than the diagnostic reference time (T_MAX).

This means that the oxygen sensor diagnosis index (VLS_CYC_AFR) for each engine operation region is different for the same response delay of the oxygen sensor, and although the actual oxygen sensor response delay time is Σ (T_REAL-T_MAX) = -0.15s The oxygen sensor is determined to be abnormal.

The present invention has been made in order to solve the above problems, it is possible to more properly calculate the average diagnostic index of the oxygen sensor diagnostic index for determining whether the oxygen sensor is abnormal abnormality, according to the change in the operating area of the engine The purpose of the present invention is to provide a method for diagnosing the oxygen sensor of an engine to solve the problem of non-uniformity of the individual oxygen sensor diagnosis index and to reduce the error rate of the oxygen sensor by more appropriate diagnosis of the response delay of the oxygen sensor.

Oxygen sensor diagnostic method of the engine of the present invention for achieving the above object is

In the method of diagnosing the oxygen sensor of the engine for determining whether the oxygen sensor is abnormal abnormally based on the output signals of the oxygen sensor measured at least two specified times,

Oxygen sensor measured and T_MAX obtained by adding T_NOR_RICH of the normal oxygen sensor at the engine speed and load, and response delay time (T_DLY) of the oxygen sensor as the basis of error determination Accumulating the rich section T_REAL by the specific number of times and obtaining the cumulative diagnostic reference time SUM_T_MAX and the cumulative actual rich section SUM_T_REAL, respectively;

Obtaining an average diagnosis index by dividing the cumulative actual rich section SUM_T_REAL by a cumulative diagnosis reference time SUB_T_MAX;

And determining whether the oxygen sensor is abnormal abnormally according to whether the average diagnostic index is greater than one.

Obtaining the cumulative diagnostic reference time (SUM_T_MAX) and the cumulative actual rich section (SUM_T_REAL), respectively, is preferably performed only when the engine speed and the load satisfy an oxygen sensor diagnosis condition that does not change rapidly.

The oxygen sensor response index can be solved by solving the problem of non-uniformity of the individual oxygen sensor diagnosis index according to the change of the engine operating area by calculating the average diagnosis index of the oxygen sensor diagnosis index to determine the abnormal abnormality of the oxygen sensor. A more appropriate diagnosis of the delay can reduce the false positive rate of the oxygen sensor.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

2, an exemplary embodiment of the present invention is a diagnostic criterion obtained by adding a rich section T_NOR_RICH of a normal oxygen sensor at a corresponding engine speed and a load and a response delay time T_DLY of an oxygen sensor serving as an error determination standard. Accumulating the time T_MAX and the rich section T_REAL of the oxygen sensor actually measured by the specific number, respectively, to obtain the cumulative diagnostic reference time SUM_T_MAX and the cumulative actual rich section SUM_T_REAL, respectively;

Obtaining an average diagnosis index by dividing the cumulative actual rich section SUM_T_REAL by a cumulative diagnosis reference time SUB_T_MAX;

And determining whether the oxygen sensor is abnormal abnormally according to whether the average diagnostic index is greater than one.

Here, the step of obtaining the cumulative diagnosis reference time (SUM_T_MAX) and the cumulative actual rich section (SUM_T_REAL), respectively, is performed only when the engine speed and the load satisfy the oxygen sensor diagnosis condition that does not change rapidly.

That is, the engine rotation speed and the load condition satisfy the oxygen sensor diagnosis condition until the counter reaches a certain number of times, the number of which is set in the range of approximately 100 or more hundreds while using the counter. The cumulative diagnostic reference time (SUM_T_MAX) and the cumulative actual rich section (SUM_T_REAL) are obtained and divided, respectively, to obtain an average diagnostic index for determining the normality of the oxygen sensor.

When the example of Table 1 described in the background art is judged according to the present invention, since ΣT_REAL = 3.3s and ΣT_MAX = 3.45s, VLS_CYC_AFR_MV = ΣT_REAL /ΣT_MAX=3.3/3.45 = 0.956 <1, and the oxygen sensor is diagnosed as normal. .

In other words, in the prior art, ΣT_REAL <ΣT_MAX, and only 6 times during the diagnosis, T_REAL was greater than T_MAX, but the oxygen sensor was determined to be abnormal. Considering the T_MAX value, the diagnostic index value is also appropriate.

Of course, in the case of the abnormal oxygen sensor, since T_REAL has a larger value each time than T_MAX, the accumulated T_REAL is larger than the accumulated T_MAX, and VLS_CYC_AFR_MV is larger than 1, so it is determined that the oxygen sensor is abnormal normally. Oxygen sensor diagnostics have equivalent results. That is, the present invention reduces the error rate of diagnosis of the normal oxygen sensor.

1 is a flowchart illustrating a method for diagnosing an oxygen sensor of an engine according to the prior art;

2 is a flowchart illustrating a method of diagnosing an oxygen sensor of an engine according to the present invention.

Claims (2)

In the method of diagnosing the oxygen sensor of the engine for determining whether the oxygen sensor is abnormal abnormally based on the output signals of the oxygen sensor measured at least two specified times, Oxygen sensor measured and T_MAX obtained by adding T_NOR_RICH of the normal oxygen sensor at the engine speed and load, and response delay time (T_DLY) of the oxygen sensor as the basis of error determination Accumulating the rich section T_REAL by the specific number of times and obtaining the cumulative diagnostic reference time SUM_T_MAX and the cumulative actual rich section SUM_T_REAL, respectively; Obtaining an average diagnosis index by dividing the cumulative actual rich section SUM_T_REAL by a cumulative diagnosis reference time SUB_T_MAX; Determining whether the oxygen sensor is abnormal or not according to whether the average diagnostic index is greater than one; Oxygen sensor diagnostic method of the engine, characterized in that configured to include. The method according to claim 1, The step of calculating the cumulative diagnostic reference time (SUM_T_MAX) and the cumulative actual rich section (SUM_T_REAL), respectively, is performed only when the engine speed and the load satisfy an oxygen sensor diagnosis condition that does not change rapidly. Oxygen sensor diagnostic method of the engine, characterized in that.

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